The present invention relates to a device for forming perforations in bar-shape articles utilising laser rays.
The present invention finds particularly advantageous application in the fields of production of smoking articles, in particular cigarettes, to which the following discussion will make specific reference without loss of generality thereby.
For the purpose of avoiding any doubt about the interpretation of various terms utilised in the following description and claims, it is stated that:
the term "focal length" is to be understood as relating to the distance travelled by a beam of focused laser rays between the zone of emission and the focus; and PA1 the term "piercing point" is to be understood as the point at which it is required to form a hole.
In the manufacture of cigarettes it is known to make so-called "ventilated" cigarettes, that is to say cigarettes provided in the region of the filter, with a plurality of holes acting to permit the smoker to draw in a percentage of fresh air together with the smoke, with the double advantage of diluting the inhaled smoke and reducing the temperature and therefore the content of harmful elements.
In the past, to manufacture ventilated cigarettes, needle devices have been used the efficiency of which has become ever reduced with the increase in the productive capacity of cigarette making machines. In fact, if associated with relatively high speed cigarette making machines, the said needle devices wear out in a relatively short time causing frequent interruptions in the productive cycle.
For the reasons explained above the said needle devices have recently been replaced, when possible, by laser ray perforation devices which have been made in one of two different constructional arrangements. In the first of these above mentioned known constructional arrangements a beam of laser rays is emitted in pulses by a fixed laser generator and directed on to a cigarette to be pierced. This latter, during the piercing operation, is made to rotate on itself in such a way that the holes formed in it are distributed in a substantially uniform manner around at least one circumference.
In the other of the two above mentioned known constructional arrangements a laser of high power is used which, for the piercing of each cigarette, emits a single beam of rays which is decomposed by fixed reflectors into a plurality of beams equal in number to the holes to be formed. In this case the holes in each cigarette are made simultaneously without it being necessary to make it turn about its axis.
Both of the two above described known constructional arrangements have significant disadvantages which render practical embodiments problematical. In fact, the first constructional arrangement necessarily requires that each cigarette is rolled between two facing surfaces in such a way as to turn about its axis. Since the cigarettes have already been "softened" following a first rolling performed during the operations involved in connection of a filter, a further rolling to perform the piercing is particularly damaging in that it certainly involves a partial emptying of the cigarette. The second of the two constructional arrangements described above is, on the other hand, difficult to put into practice for purely economic reasons given the high power and, therefore, the high cost of the laser which must be used.